Sealing plastic film

ABSTRACT

A method of heat sealing layers of plastic film wherein the film layers are heated in contact until the plastic attains a flowable state, and the area of flowable plastic is then extended until the plastic separates. The molten plastic then retracts towards the unheated flank of the seal area to form matching bead seals. The method is applicable to automatic bagmaking machines.

0 United States Patent 1151 3,640,790 Rowley et al. 1 Feb. 8, 1972 [54]SEALING PLASTIC FILM [56] References Cited [72] Inventors: EdwardKenneth Rowley, Beloeil Station, UNITED STATES PATENTS Quebec; ClaytonThomas Waugh, Montreal, Quebec, both of Canad 3,562,053 2/1971 Lmdley 156/251 3,115,564 12/1963 Stacyl ...156/25l X 1 1 Asslgnw Cmdwn lndusmes1111mm! Montreal, 3,441,460 4/1969 Carmichael... ..156/251 Quebec-Canada 3,531,359 9/1970 v Jones et al. ..l56/5l5 [22] Filed: Apr. 23,1970 Primary ExaminerReuben Epstein [2|] AppLNo-i 311229AttameyAlexanderO.McIntosh 301 Foreign Application Priority am 1571ABSTRACT May 21, 1969 Canada ..052,1 61 A method of heat Sealing layersof Plastic film wherein the film layers are heated in contact until theplastic attains a flowable [521 us. (:1 ..l56/25l,156/515 State, and thearea of flowable Plastic is then extended until [5 1] Int. Cl ..B32b 31/18 the Plastic Separates- The molten Plastic enacts towards [53] theunheated flank of the seal area to form matching bead Field of Search156/251 seals. The method is applicable to automatic bagmaking machines.

4 Claims 3 Drawing Figures 17 I I I I I I I I 7 A I Y 2 a Q a PMENIEBFEBamz 3.640.790

INVENTORS Edward Kenneth ROWLEY Clayton Thomas WAUGH AGENT SEALINGPLASTIC FILM This invention relates to a method for heat sealing plasticfilm.

In the manufacture of containers such as bags from plastic film, it iscommon practice to form the container joints by welding or heat sealingthe plastic film. The strength of the finished container depends to alarge extent upon the strength of the seal joining its component parts.A strong seal requires a melting together of the contacting surfaces ofthe plies of film being sealed without weakening of the adjacent partsof the film. weakening of the seal border may be avoided by cooling thefilm adjacent to the seal or by melting together in bead form theadjacent edges of the film. The latter can be carried out by a hot bladeor hot .wire sealer. However, there are operational advantages toemploying sealer bars that during sealing also clamp in place the pliesof film being sealed. These, however, give a weaker flange-type sealratherthan a bead seal joining the edges of the sealed film.

It has now been found that a bead-type seal can be formed between pliesof heat-sealable film employing heated sealer bars if, subsequent to thesea] area of the film attaining a state of flow, the heated sealer baris removed and the seal area while still in a flowable state is extendeduntil the flowable plastic in the seal area separates. The plastic inthe area of the seal is found to form a bead along the border of thejoined plies of film. This method of forming bead seals can be carriedout employing normal sealer bars if the bars are operated at atemperature that gives highly molten plastic and if the sequence of thesealing step is modified to cause extension of the seal area while it isstill in a highly flowable state. The novel sealing method provides astrong narrow seal which is particularly applicable to the fabricationof plastic bags.

It is therefore the primary object of this invention to provide a methodfor forming bead-type seals between plies of heatsealable film.Additional objects will appear hereinafter.

The sealing method of this invention comprises the steps of l. heatingplies of plastic film in contact at the position of the seal until theplastic attains a molten flowable state, the flanks of the seal positionbeing unheated,

2. extending the hot flowable plastic freely until it separates, and- 3.allowing the separated edges of the hot plastic to freely retracttowards the unheated flank of the seal area, thus forming the bead seal.

The formation of the bead seal is illustrated in the accompanyingdrawings wherein FIG. I is a diagrammatic vertical section of two pliesof film compressed between a sealer bar and anvil;

FIG. 2 is a diagrammatic vertical section showing the extension of theheated seal area of the film of FIG. 1; and

FIG. 3 is a diagrammatic vertical section showing the film of FIG. 2with a completed bead seal.

In FIG. 1 two layers of heat-scalable plastic film 1 and 2 are showncompressed between anvil 3 and heated sealer bar 4. Sealer bar 4 iscarried by support 5, of heat insulating material, which is movable in avertical sense. Nip rolls 6, 7 and 8, 9 control the passage of the filmthrough the sealing apparatus. Sealer bar 4 is kept in contact with thelayers of film until the region of film adjacent to the sealer bar'facehas reached a flowable state. The anvil 3 may also be heated. The facesof the anvil and sealer bar will be provided with a coating that avoidsadherence of the hot film.

The heated sealer bar is next raised as shown in FIG. 2 and concurrentlythe heated region of the film is extended through flow back towards theunheated flanks of the seal as shown in FIG. 3. This forms two beadseals 11 and 12.

The making of effective bead seals depends upon correlation between theoperation of the sealer bar and the operation of the seal extensionmeans. The film must be drawn out when it reaches a suitable degree offluidity. A continuous seal of appreciable length can be made in minimumtime only if uniform heat transfer conditions exist. It will beunderstood by one skilled in the art that adjustment of the sealer bartiming and seal extension will vary with thickness and type of filmbeing sealed.

The speed with which the film layers to be sealed are brought to asuitable state of fluidity can be increased if the anvil 3 is replacedby a second sealer bar. This arrangement can also result in thenarrowing of the region of film that is melted.

The seal extension means may comprise two sets of nip rolls located oneach side of the sealer bar, as shown in the drawings, and driven incooperation with the operation of said sealer bar. One set of theserolls may be the drive rolls of a conventional heat sealing unit and theother a set of rolls operating on the output side of the sealer unit.Other means of drawing out the seal region are possible, such asplungers that thrust against the film at the flank of the seal or doublebelt film transports accepting the output from the sealer unit. It isessential that the operation of these seal extension means becoordinated with the operation of the sealer bar unit. The apparatus canform an element of a conventional bagmaking machine serving toconcurrently seal and sever plies of plastic film.

The method of this invention can be employed to seal plastic film thatmelts when heated. It is particularly adapted for use with film formedfrom a polyolefin such as polyethylene and polypropylene.

The method of this invention provides a means for forming bead sealsbetween layers of heat-sealable film through modification of theoperation of conventional machines employed for fabricating plastic bagsby heat sealing of films.

What we claim is:

1. A method for heat sealing plies of plastic film comprising a. heatingthe plies of plastic film in contact at the position of the seal bycompressing the plies of plastic film between a heated sealer bar and ananvil until the plastic between the sealer bar and the anvil attains amolten flowable state, the flanks of the seal position being unheated,

b. removing the sealer bar from the position of the seal,

0. extending the heated flowable plastic freely until it separates, and

d. allowing the separated edges of the heated plastic to freely retracttoward the unheated flank of the seal area, thus forming a bead seal.

2. A method as claimed in claim 1 wherein the film is formed frompolyethylene or polypropylene.

3. A method as claimed in claim 1 wherein the heated plastic at the sealposition is extended by means engaging the unheated flanks of the seal.

4. A method as claimed in claim 1 which constitutes a step in a processfor the manufacture of plastic bags.

2. A method as claimed in claim 1 wherein the film is formed frompolyethylene or polypropylene.
 3. A method as claimed in claim 1 whereinthe heated plastic at the seal position is extended by means engagingthe unheated flanks of the seal.
 4. A method as claimed in claim 1 whichconstitutes a steP in a process for the manufacture of plastic bags.